Recently, the use of flat display panels has increased, a liquid crystal display (LCD) being a representative flat display panel.
Generally, unlike an existing cathode ray tube (CRT), such an LCD requires a backlight module that provides light uniformly to an entire screen.
Specifically, such a backlight unit has a configuration providing light uniformly to a rear surface of the LCD and is configured such that a light source, i.e. a light-emitting diode (LED), is disposed along an edge of a light guide plate, and the light guide plate includes a reflective plate on a lower surface thereof to transfer light generated by the light source upwardly.
In the aforementioned configuration, the light generated by the light source is transferred upward by the light guide plate and the reflective plate, and the transferred light is uniformly transferred upwardly through a light-condensing sheet.
A sheet having a general prism formed therein may be used as the light-condensing sheet.
In addition thereto, when a separate reflective polarizer sheet is provided on an upper portion of the light-condensing sheet, brightness of the LCD can be improved.
As described above, the backlight unit is configured such that the light generated by the light source provided on the one side surface is transferred upwardly by the light guide plate and the reflective plate and the transferred light is uniformly condensed through the light-condensing sheet.
Meanwhile, when the backlight unit includes a reflective polarizer sheet, the brightness of the LCD can be considerably increased. Thus, the reflective polarizer sheet is widely used. However, when the light-condensing sheet having a plurality of prisms and the reflective polarizer sheet are bonded to each other, an upper tip portion of each of the prisms having an inclined surface may disappear while forming a bonding surface.
As described above, in the case that the upper tip portion of each of the prisms disappears and forms the bonding surface, the reflective polarizer sheet and the light-condensing sheet are bonded to each other, so that the reflective polarizer sheet and the light-condensing sheet can maintain a stable bonding state.
However, since an upper end portion of the light-condensing sheet disappears due to a bonding with the reflective polarizer sheet, a portion forming a bonding surface, i.e. an inclined surface disappears. Thus, efficiency, in which the light-condensing sheet condenses light transferred through a low portion thereof, is lowered.
In particular, when light passes though the bonding surfaces between the reflective polarizer sheet and the prisms, a line of the bonding surface is visible or a color shift phenomenon is generated, due to an optical interference phenomenon occurring in the reflective polarizer sheet formed from a multi-layered film. Thus, screen quality of a display is lowered, and an unintended Moire Phenomenon may be generated, due to optical interference with a liquid crystal panel.